if anyone wants to paint plasic, interior plastic included, this is the best way i have found for it.

I dont sand it... clean it, scuff it, prime it like 5 times... (just use a scuff pad to score the layers of primer, not sand paper yet) but whatever you do. DONT break the surface of the plastic, score it with a scuffy pad... but DONT break it... then when you have enough layers of primer where you can sand it smooth, THEN paint it, clear it... and where you want to go from there is up to you... (Wet sanding, polishing...) well if the clear is good enough, you should just be able to install after.

Oh, and lots of people think drying paint in the sun is better, maybe on metal. but on plastic it makes it softer. dry it in a warm, but shady place, with LOTS of air flow... airflow is key.